1. Field of the Invention
The invention relates to a device for controlling the flow rate of hydraulic fluid in a supply line to the cylinder chambers of suspension cylinders in vehicles, especially tractors, having a permanent suspension axle, whose height is regulated by a level control device, a choke being inserted into the supply line for limiting the flow rate of the hydraulic fluid.
2. Description of Related Art
From German Patent 42 42 448, a hydropneumatic suspension device is known for vehicles having high load-bearing requirements and having a load-sensing pump as a pressure supply, in which static load changes are compensated for by increasing and decreasing control processes. The dynamic position change is measured by electrical sensors and is conveyed to the level control device as an averaged signal. To adjust the control speed, a choke, through which fluid can flow in both directions, is inserted into the supply line leading to the suspension cylinder circuit. However, this choke is an obstacle for rapid pressure adjustment in response to large load changes.
An improvement is achieved by the device described in German Patent 197 19 075 A1, which, in the decreasing control mode, makes possible an essentially identical volume flow, thus, at the same time, making possible the decreasing control processes, irrespective of the varying static pressure level. This solution makes it possible to use a larger control nozzle, which permits higher control quantities at lower axle loads, thus shortening the adjusting times. When the vehicle axle reaches the limit stops in particularly high load changes, this measure is not sufficient.
It is an object of the invention to create a suspension concept that, in response to load changes, keeps the adjustment times short, up to point of reaching the limit stops. It is a further object of the invention to provide such a suspension design that is comfortable and soft overall.
These and other objects of the invention are achieved in a device for controlling the flow rate of hydraulic fluid in a supply line to the cylinder chambers of suspension cylinders in vehicles, especially tractors, having a permanent suspension axle, whose height is regulated by a level control device, a choke being inserted into the supply line for limiting the flow rate of the hydraulic fluid. According to the invention, the supply line is provided with a bypass line that circumvents the choke, an auxiliary choke, controlled by a control unit via level sensors, being inserted into the bypass line, the auxiliary choke being switched on in response to pronounced static load change when the limit stops of the vehicle axle have been reached, thus permitting a larger flow rate of the hydraulic fluid. As a result of this measure, adjusting times in the accumulator are shortened. Using the bypass line, the pressure adjustment is carried out in a rapid and short-term manner. As soon as the pressure adjustment is completed and the vehicle axle has moved slightly from its limit stops, the auxiliary choke is closed once again and the further control process can be carried out, for example in the manner indicated in German Patent 197 19 075. The level control device can be set so that it disconnects the auxiliary choke as soon as the vehicle axle has moved from its limit stop by at least two millimeters. In this manner, the accumulators can be filled up or emptied to the required load pressure more rapidly.